NGN (Next Generation Network) is a hot spot of research in the field of communication standards at present. It adopts IP or any other packet technology as a bearer network technology to make fixed communications and mobile communications converged. An NGN can provide more abundant multimedia services, for example, emerging services with real-time demands (such as VoIP, video conference, distance multimedia education and video-on-demand), which require the communication network to provide efficient end-to-end QoS (Quality of Service); and meanwhile, users are raising their demands on network QoS. Therefore, how to provide end-to-end QoS will become one of the core issues of an NGN.
ITU-T (International Telecommunication Union-Telecom) is the telecommunication standardization sector of ITU (International Telecommunication Union). It has formulated standards for resource and admission control. In the latest draft of RACF (Resource and Admission Control Functions) promulgated by ITU-T in May 2008, the functional architecture of RACF is provided, as shown in FIG. 1, the RACF consists of two parts: a PD-FE (Policy Decision Functional Entity) and a TRC-FE (Transport Resource Control Functional Entity).
The PD-FE has nothing to do with transmission technologies and SCF (Service Control Functions). The PD-FE makes a final decision on resource and admission control based on network policy rules, service information provided by the SCF, transport layer subscription information provided by NACF (Network Attachment Control Functions), and a resource availability decision result provided by the TRC-FE.
The TRC-FE has no relationship with services, but does with transmission technologies. The TRC-FE is responsible for collecting and maintaining transmission network information and resource status information. After receiving a resource request from the PD-FE, the TRC-FE executes resource-based admission control based on QoS, priority demands, resource availability information and transport-related policy rules.
The transport layer consists of a PE-FE (Policy Enforcement Functional Entity) and a TRE-FE (Transport Resource Enforcement Functional Entity). The PE-FE is a packet-to-packet gateway and may be located between a CPN (Customer Premises Network) and an access network, or between an access network and a core network, or between networks of different operators, and serves as a key node for supporting dynamic QoS control, port address translator control and NAT (Network Address Translator) transversal. The TRE-FE executes the transport resource policy rules sent from the TRC-FE, with the range and function thereof as well as an Rn interface remaining to be studied, and the study is not in the research scope in R2 stage.
PD-FE
The PD-FE is a policy decision functional entity. It makes a preliminary decision on QoS resources based on media stream session information (acquired from the SCF via an Rs interface), and transport resource subscription information of users (acquired from the NACF via an Ru interface), and then interacts with the TRC-FE to determine whether there are sufficient QoS resources, and finally makes a final admission decision and sends the decision to the PE-FE for execution.
TRC-FE
The TRC-FE is mainly responsible for resource control. It monitors resources in a network and collects related information, and makes a response according to a specific resource condition when the PD-FE requests resources.
PE-FE
The PE-FE mainly performs policy control (gate control, bandwidth, traffic classification and tagging, traffic shaping, layer 2 and layer 3 QoS mapping, and collection and reporting of resource-use information, etc) under the direction of the PD-FE.
TRE-FE
The TRE-FE is currently defined to execute a layer 2 policy under the direction of the TRC-FE, but the specific functions and scope are yet to be determined.
A resource request process in PUSH mode in the prior art is shown in FIG. 2. The process includes the following steps:
(201) SCF receives or generates a service signaling message which triggers the SCF to generate a resource initialization request;
(202) the SCF sends a resource initialization request message to a PD-FE, to request authorization and reservation of QoS resources, wherein the message includes a media stream description, QoS parameters and other information;
(203) the PD-FE authorizes the requested QoS resources, i.e. checking whether the requested resources are consistent with policy rules of local operators and transport subscription information in NACF;
(204) if the authorization check is passed, the PD-FE locates and determines the access network and core network the media stream involves in, and moreover, the PD-FE interacts with a TRC-FE, and checks the resource availability of the involved networks;
(205) the PD-FE makes a final admission decision based on Step (203) and Step (204);
(206) if the final admission decision is passed, the PD-FE will send a policy installation message to a PE-FE;
(207) the PE-FE sends a policy install answer message to the PD-FE to confirm installation; and
(208) the PD-FE sends a resource initialization answer to notify the SCF.
In Step 206, the policy installation message sent from the PD-FE to the PE-FE may include a plurality of policies. If an error occurs in the installation of some policies, then the policy install answer message in Step 207 will include the names and status of the error policies, that is to say, if an error occurs in the installation of some policies, the policy install answer message will only give a message-level error reason. Typically, it is expressed with a [Experimental-Result] parameter.
In the prior art, a policy installation condition is expressed with the following parameters in the PIA (Policy Install Answer) message:

In this case, a coarse-grained (message-level) error reason is reported. This is not favorable for accurate acquisition by the PD-FE of the detailed information of the policy installation enforced by the PE-FE.